Compression heat pumps, which employ an HCFC-family refrigerant such as an R22 refrigerant, have been used widely in refrigeration apparatus of air conditioning systems or the like. Such a refrigeration apparatus has a refrigerant circuit formed of a combination of a compressor, a heat source side heat exchanger, an expansion valve, and a use side heat exchanger that are connected together by refrigerant piping.
In recent years, there have been strong demands for air conditioning (cooling and heating), especially for large-scale air conditioning systems for office buildings or the like (hereinafter referred to as the building air conditioning system). A typical building air conditioning system usually comprises a single outdoor unit and a plurality of indoor units installed in individual rooms of a building. The outdoor unit and the indoor units are linked together by refrigerant lines (piping) that extend from the outdoor unit to every room throughout the building.
Recently, a great concern has developed for global environmental protection, requesting environmentally friendly refrigerants (e.g., HFC-family refrigerants) be utilized as a replacement refrigerant for a currently used refrigerant of the HCFC family (e.g., an R22 refrigerant). This will give rise to the necessity of replacing a currently used refrigerant with an environmentally friendly refrigerant in building air conditioning systems.
In cases where HFC-family refrigerants are utilized, a synthetic oil, such as ester oil and ether oil, is employed as a refrigeration oil. These synthetic oils compare poorly in stability with a mineral oil conventionally used in an HCFC refrigeration apparatus, so that it is likely that a sludge-like solid material (contamination) is deposited. The use of an ester or ether oil therefore requires severe moisture and contamination control.
A large-scale building air conditioning system requires extensive refrigerant piping work because it is necessary to arrange a great number of refrigerant lines from the outside to each room of the building. Such piping work is time and cost consuming. If the existing refrigerant piping can be reused when replacing HCFC with HFC, this favorably achieves reductions in construction cost and time in comparison with cases where a new air conditioning system is constructed. PROBLEMS TO BE SOLVED
In the case an existing refrigerant circuit is reused, replacing an HCFC-family refrigerant with an HCF-family refrigerant in the foregoing refrigeration apparatus produces the following problems.
Large-scale building air conditioning requires lengthy refrigerant piping. Therefore, moisture and contamination should be controlled extremely severely over a wide range. The exertion of such control is very difficult.
The existing refrigerant piping requires a thorough cleaning. This is considerably time and cost consuming.
In some cases, a refrigeration oil, used as a compressor lubricating oil, is deposited on the inside wall of a refrigerant line. When replacing a refrigerant of one type in a refrigerant circuit with a refrigerant of a different type, it will become necessary to thoroughly clean each refrigerant line.
Conventional HCFC refrigeration apparatus use a mineral oil as a refrigeration oil. On the other hand, an HFC refrigeration apparatus uses a synthetic oil (e.g., an ester oil and ether oil) as a refrigeration oil. These synthetic oils compare poorly in stability with a mineral oil, and a contamination is deposited when mixed with a mineral oil. This means that a slight amount of mineral oil left in a refrigerant line results in deposition of a contamination, therefore exerting undesirable effects on the refrigeration operation. In the case an HCFC-family refrigerant is replaced by an HFC-family refrigerant, the refrigerant lines must be thoroughly cleaned.
Complete removal of a mineral oil from in a refrigerant line by cleaning (flushing) is considerably time and cost consuming.
Another problem resulting from the exchange of a currently used refrigerant for the new environmentally safe refrigerant is the compressive strength of existing refrigerant lines, since their compressive strength is usually insufficient for the new refrigerant to replace with the old one. The refrigerant line design pressure is 28 kg/cm.sup.2 for the R22 refrigerant which is an HCFC-family refrigerant. On the other hand, it is 34 kg/cm.sup.2 for the R407C refrigerant which is an HFC-family refrigerant. The introducing of an R407C refrigerant into the existing refrigeration apparatus may produce the problem that the existing refrigerant piping is poor in pressure resistance. It is therefore impossible to compress the refrigerant to a region of specified high pressure level. If the refrigerant is compressed to such a high level, the refrigeration apparatus is not operationally safe.
It has been considered that it is difficult for the existing HCFC refrigerant piping to be reused for an HFC refrigeration apparatus.
Bearing in mind the above-described difficulty resulting from reusing the existing HCFC refrigerant piping for an HFC refrigeration apparatus, the present invention was made. Accordingly, an object of the present invention is to eliminate the necessity of exerting extremely severe moisture and contamination control which has been conventionally required when using HFC-family refrigerants. Another object of the present invention is to make it possible to reuse the existing refrigerant piping.